Hi Rick,
For your first question, I understand that you want to use your custom domain in your email address instead of domain name onmicrosoft.com to send emails.
Generally, if you want to use your custom domain in your Office 365 account, you should first verify and add your custom domain in your Office 365 account.
To verify and add the domain name you want to use in your Office 365 account. For detailed steps, you can refer to :
Add your domain to Office 365
http://onlinehelp.microsoft.com/en-us/office365-smallbusinesses/ff637561.aspx
After adding your custom domain name, you can do the steps below to change your email address from xxx@domain.onmicrosoft.com to xxx@yourdomain.com
Sign in your Office 365 portal -> Click Admin -> Click your company name on the left corner -> Click Edit -> Click the drop-down list to select the custom domain you want to use in the Default domain part.
In addition, you can refer to the following article to check if it corresponds to your situation.
Simple Domain Sharing for SMTP Email Addresses: http://community.office365.com/en-us/wikis/exchange/simple-domain-sharing-for-smtp-email-addresses.aspx
For your second question, I understand that after you downloaded desktop integration app and lync app, your computer froze on startup though you have go into safe mode and use system restore.
Based on this situation, this issue may be caused CPU and any other issues about your system. You can go to the task manager to check if it is caused by specific processes. Generally, this issue is more related to Windows support. I think Windows Forum is the best suit to help you. You can post a new thread about this issue in the forum.
Here is the link: http://social.technet.microsoft.com/Forums/en/w7itproperf/threads
Thanks,
Vivian Wang